Solvent extraction



April 15, 1958 T. D. NEVlTT 2,831,039

- SOLVENT EXTRACTION Filed April 4,- 1955 a gm A M 3;? In

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m E &, INVENTOR. Thomas D. Nev/ff and (M) A TTORNE Y aid ()il Company, Chicago, iii, a corporation oi indiana i Application April 4, 1955, Serial No. 493309 5 Claims. ((11. roe-m This invention is concerned with the separation of mixtures of hydrocarbons by means of selective solvents. More specifically, this invention is concerned with the separation of mixtures of hydrocarbons into fractions of diverse structural types by solvent extraction with certain dialkyl sulfones.

The use of solvent extraction for the separation of mixtures of hydrocarbons has long been known. This method of purifying hydrocarbon mixtures takes advantage of the ditlerences in solubility of various hydrocarbon types in solvents or ample, aromatic hydrocarbons can be separated from paraflinic hydrocarbons by extraction with a number of well known solvents. Saunders (Ind. Eng. Chem. 43, 121 (1951)) has reported his study of many such solvents, and has recommended several nitriles such as beta, 3

beta-oxydipropionitrile for the separation of aromatics and nonaaromatics. Wilkes, in U. S. Patent No. 2,439,534 (1948) has proposed nine solvents oi the same class, i. e. nitriles. Kurtz, lr., in U. S. Patent 2,033,942 has proposed the selective extraction of naphthenie (low V. I.) hydrocarbons from mixtures thereof with paraffinic hydrocarbons in viscous oil mixtures such as lubricating oil fractions by the use of aliphatic sulfones, specifically dipropyl and dibutyl sulfones.

With the commercial development for producing aromatic hydrocarbons boiling within the gasoline boiling range by cyclization-dehydrogenation of paraffinic hydrocarbons and by the dehydrogenation of cycloalkanes, there has come an increased demand for processes to separate and concentrate the aromatic hydrocarbons thus produced. Thus, with the commercial development of such processes as hydroforming, platinum catalyst reforming of naphthas and the like, a tremendous potential has been created for the production of nitrationgrade aromatics such as benzene, toluene and xylenes for use by both the petroleum and chemical industries.

In accordance with my invention, mixtures of aromatic and aliphatic hydrocarbons, particularly non-viscous neutral oils, are separated into various fractions by means of fractional extraction with certain low molecular weight dialkyl sulfones. Such non-viscous neutral oils may be commercially produced as processed or unprocessed petroleum oils or mineral oils, coal tar oils, shale oils, and the like or by methods described above for the synthetic production of aromatic hydrocarbons. By the term non-viscous neutral oils is meant a neutral oil of viscosity below 135 seconds Saybolt Universal at 100 F, and generally below 50 seconds Saybolt Universal at 100 F. Such neutral oils are further characterized as boiling in the range of a petroleum naphtha stock, that is having a distillation end-point of about 450 F.

It is an object of my invention to provide a process for the selective extraction of non-viscous hydrocarbon mixtures with certain low molecular weight dialkyl sulfones. Another object of my invention is to provide for the employment of certain low molecular weight dialkyl mixtures of solvents. For exof new processes ice id sulfones in a process for theselective extraction of arcmatic hydrocarbons 7 thereof with aliphatic hydrocarbons, particularly saturated hydrocarbons. A further object is to provide processes for the concentration and purification of aromatic hydrocarbons; particularly .those containing not more than about 10 carbon atoms per molecule.v Another object is to provide a process for the separation of closeboiling or azeotro-pic mixtures of hydrocarbons by selective extraction with certain low molecular weight dialkyl sulfones. Yet another object is to provide a process for refining hydrocarbon oils 'byextraction with certain low molecular weight sulfones. These and 7 other objects of my invention WillbECODJB apparent from the ensuing I andfrorn the appended figure which description thereof is a schematic flow sheet illustrating my process.

I haveniade the remarkable discovery that only dialkyl sulfones containing 2 to 4 carbon atoms, inclusive, in the molecule and having a maximum alkyl chain length of 2 carbon atoms are effective for the selective extraction of aromatic hydrocarbons from other hydrocarbons,

- particularly saturated hydrocarbons, boiling in the gasoline boiling range. Although methyl propyl sulfone, like diethyl sulfone, contains 4 carbon atoms per molecule, it is ineffective for selective extraction of aromatic hydrocarbons in my process, as Will be shown hereinafter. I have found that sulfones having more than four carbon atoms in the molecule are completely miscible withthe non-viscous neutral oils from which it is desired to sepa rate the aromatic constituents, whereas the sulfones employed in the process of my invention readily form two phases in admixture with such feed stocks, thus permitting the separation of an extract phase and a raihnate phase.

I have further made the discovery that the addition of small amounts of auxiliary solvents such as water, increases the selectivity of the solvents of my invention for aromatic compounds. I have further observed that the addition of small amounts of Water to a sulfone having more than four carbon atoms results in the separation, when the solvent is contacted with a hydrocarbon mixture, of a second phase Which is essentially pure Water, so that no aromatics extraction is effected.

The dialkyl sulfones used in my invention are Water soluble, high boiling substances which may be either liquids or low melting solids at ordinary temperatures and pressures. They are colorless, odorless and neutral compounds, of great stability both to chemical reagents and to pyrolysis. They are readily prepared by the action of a variety of oxidizing agents upon the corresponding sulfides or sulfoxides. The melting points and boiling points of a number of these compounds are given in Table I.

TABLE I Physical properties of some low M.

W. sulfoncs M. PL, B. PL, 0. n o.

Dimethyl sulfone 109 238 Methyl ethyl sulfono. 36 Diethyl sulione 70-71 248 The above sulfones or their mixtures are useful for the separation of monocyclic aromatic hydrocarbons such as benzene, toluene, xylene or the like from mixtures containing the same. They are effective in separating an aromatic fraction from a mixture containing more than one aromatic compound, and their effectiveness is not limited by the concentration of aromatic hydrocarbons from homogeneous liquid mixtures.

and the like. In general, such line boiling range, and consist having a molecular weight range mixtures are in the gasoof hydrocarbon mixtures of 72 to 200.

The sulfones of this invention may be employed by themselves singly or as mixtures of two or more. They may be employed in aqueous solution or in conjunction with various other diluents which will affect their solvent power for aromatics. Such diluents are partially or completely miscible with water, and generally contain hydroxy groups, although this is not a limitation. Such diluents may be effective in modifying "the solvency, while avoiding the corrosivity characteristic of water. Among the diluents or auxiliary solvents may be mentioned glycerol, ethylene glycohdiethylene glycol, pentaerythritol, andthe like. Since the sulfones are extremely stable and chemically inert materials, diluents having acidic or basic characteristics may also be employed. Examples of such materials are formic acid, lactic acid, ethanolamines such as mono-, di-, and triethanolaminc and the like. Other examples of the sulfolanes, dimethyl sulfoxide, such as acetonitrile, bis-Z-cyanoethyl ether and the like; ethers or glycol ethers, tetrahydrofuran and the like; beta, beta-oxydipropionitrile, beta, beta-thiodipropionitrile and the like; halogenated hydrocarbon solvents; esters of monocarboxylic acids and dicarboxylic acids; neutral methyl ethyl ketone, methyl iso aldehydes for example furfuraldehyde, crotonaldehyde and the like; etc. Where a diluent or co-s'olvent such as I have described is used, I prefer to use from about 0.1 to about 20% by volume thereof based on the volume of sulfone solvent employed. 7

In conducting the extraction I use an amount of solvent suflicient to form a two phase system. The proportion of solvent usually falls within the range of about 0.5 to about 50 volumes per volume of feed and preferably from about 1 to about 20 volumes of solvent based on the hydrocarbon feed to be treated. In the practice of the invention either continuous, semi-continuous, or batch operation may be employed. Known types of solvent extraction equipment can be use In accordance with my invention, I first contact the hydrocarbon feed mixture either as liquid or vapor with a suitable proportion of the sulfone in liquid condition. A liquid extract phase containing the more aromatic portion of the feedstock as well as any other polar impurities derived from the feedstock, for example, organic compounds of oxygen, nitrogen or sulfur is produced. Separation of the resultant phase and from the raflinate phase hydrocarbons of similar boiling point, but of different chemical composition and physical characteristics.

In carrying out the process of my invention I can use temperatures in the range of about C. or even less to about 200 C. Economic considerations suggest the use of temperatures of about 35 C. to about 80 C. when feasible. Sufficient pressure is maintained Within the extraction zone to prevent substantial volatilization of the hydrocarbon charging stock or solvent under the liquidliquid extraction conditions, and it is obvious that pressure and temperature are related variables in the extraction process. Usually pressures within the range of about 0 to about 100 p. s. i. g. are sufiicient, it being appreciated matization of selected petroleum hydrocarbon fraction that the particular pressure which is required in a given case can readily be determined by experiment.

In addition to the co-solvents or diluents described above, antisolvents can also be used to aid in the extraction step. Suitable antisolvents such as saturated hydrocarbons, perfluorocarbons, perlluoroamines, perfiuoroethers and the like may be used in proportions of about to about 100 volume percent of the feedstock treated, and may be added to the feedstock to be dearomatized or introduced directly into the extraction zone.

In order to more clearly understand the nature of my invention, a representative operating procedure is described in conjunction with the appended figure. The hydrocarbon mixture to be extracted, for example, a reformed naphtha fraction boiling within the range of about 40 to about 200 C., and containing benzene, toluene,

and xylenes, is charged through line 1 into heater 2- wherein the temperature thereof is adjusted to a suitable value, for example, between 40 C. and about 100 C., and is then passed into extraction zone 3. Extractor 3 may be jacketed or provided with heat exchange coils to permit maintenance of desired temperatures at various levels therein. If desired, an antisolvent such as a low boiling paraflin hydrocarbon, for example, pentane or a hexane can be introduced with the feed or otherwise in proportions of about 10 to about 100 volume percent thereof.

The solvent, e. g., methyl ethyl sulfone, is introduced through line 4 into heater 5 wherein its temperature is brought to the desired value, thence into extractor 3. If desired, an auxiliary solvent or diluent, e. g., water, can be introduced through valved line 6 into line 4 in proportions between about 1% and about by weight, based on the weight of solvent.

In the extraction zone the hydrocarbon fraction is countercurrently contacted with the solvent at temperatures of about C. to about C. at atmospheric pressure. Lower temperatures may also be used. Benzene and any other aromatic present in the charge are extracted and are removed, together with the major portion of methyl ethyl sulfone through line 7. The extract phase is passed through heat exchanger 8, and thence into stripping tower 9, preferably equipped with a conventional reboiler coil or other heating arrangement, 10. Vapors of the extracted naphtha characterized by a substantially increased aromatic content as compared with the concentration of aromatic hydrocarbons in the feed stock entering the system through line 1, are withdrawn as an overhead product from tower 9 through line 11 and condenser 12. All or a portion of the extracted aromatic material may be withdrawn through valved line 13. If desired, a portion of the extracted material may be diverted through line 14 and heater 15, thence through line 16 to the lowermost portion of extractor 3 to function as reflux, thus increasing the purity of the extract materials produced in the extraction process. The extracted aromatic hydrocarbons can be redistilled into fractions of different boiling ranges and otherwise after treated by refining methods known in the art.

Bottom product from tower covered from the extract phase hydrocarbons, predominantly aromatics. This product is removed through line 17 and all or a part thereof may be recycled through valved line 18 to line 4 for re-entry into the upper portion of extractor 3. It is desirable to remove all or a portion of the stripped solvent through valved line 19 for purification treatment before recycle to extraction. The purification may involve redistillation to remove residual hydrocarbon components of the mixture, recrystallization of the solvent, removal of auxiliary solvent therefrom by conventional means, etc.

Returning now to extractor 3, the raflinate obtained therefrom comprises a small amount of solvent and hydrocarbons characterized by a substantially reduced concentration of aromatic hydrocarbons as compared with 9 comprises solvent reand a small amount of the concentration thereof in the feed stock. The raffinate is removed from extractor 3 through line 20 to cooler 21 and thence through line 22 to washing vessel 23. The raflinate is washed in a countercurrent operation in vessel 23 with water introduced through line 24 such that raffinate free of solvent is removed overhead via line 25. Water-containing solvent comprising the bottoms product from vessel 23 is removed via line 26 to conventional apparatus (not shown) for separation of water and recovered solvent, which may then be combined with solvent re covered from tower 9 via line 19 and subjected to the purification steps above described. Rafiinate which contains any anti-solvent added with the feed in line 1, is withdrawn via line 25 for such further treatment as may be desired, including redistillation, percolation through silica gel, clays or other adsorbent solids, acid or alkali treatment, etc. If desired, a portion of the rafiinate may be recycled (by lines not shown) to the upper portion of extractor 3.

While the use of vacuum stripping to separate low boiling extracted material, having substantially lower boiling points than the sulfone solvent, is effective, it should be appreciated that the treatment indicated in the figure is merely illustrative. Any other suitable means of separating extract from the extract phase and recovering solvent therefrom may be employed. Thus the sulfone may be recovered from'the extract phase by crystallization at low temperatures, or by washing the extract layer with a solvent that is highly selective for the sulfone as for example, water, acetone, ethers, etc.

Illustrative batch extraction data are provided in Table II. In each instance the feed was a mixture of equal volumes of toluene and n-heptane. The volume ratio of solvent to feed was one. Except as indicated, extraction was efiected at 25 C. The fi-value or separation factor in the table is the molar ratio of toluene to heptane in the extract divided by the ratio of these components in the rafiinate, and corresponds to alpha, the separation factor calculated in fractional distillation processes.

TABLE 11 Wt. Percent Wt. Percent Solvent Toluene Toluene fl-Value Extracted in Extract Dimethyl Sulfone (130 0.)- 16 96. 5 23. 5 Methyl Ethyl Sulfone 32 93 14. 8 Methyl Ethyl Sulfone 5% Water" 23 96 22. 4 Dlethyl Sultone (at 70 O.) 54 83 11. Methyl n-Propyl Sulfone 70 67 3. 0 Methyl n-Propyl Sulfoue H2O 38 74 3. 03 1:1 Diethyl and Dlmethyl Sulione at 100 25 Di-n-Propyl Sulfone Homogeneous mixture 1 Elevated temperatures were required in order to maintain the higher melting dimethyl sulfone and diethyl sulione m the liquid phase.

From the table, it will be noted that methyl ethyl sulfone was an excellent selective solvent for aromatics. The addition of 5% of water to the methyl ethyl sulfone results in a decrease in the quantity of toluene extracted, but the solvent is extremely selective as will be noted from the high S-value and the high concentration of toluene in the extract. In the case of tdi-n-propyl sulfone the mixture of feedstock and solvent was found to be completely homogeneous. A mixture of 25% toluene, 25% n-heptaue, 40% di-n-propyl sulfone and 10% water was prepared at 25 C. and was found to form two layers, the lower layer containing most of the original water and little or no hydrocarbon material. It will he observed from the fi-values given in Table 11 that dimethyl sultone and methyl ethyl sulfone exhibit the greatest selectivity for aromatic extraction, and that diethyl sulfone alone or in admixture with an equal volume of dimethyl sulione gives a high extract yield as well as substantial aromatics enrichment of the extract phase. Methyl n-propyl sulfone exhibits a low li-value, in surprising contrast to diethyl sulfone which has the same C :8 ratio.

By repetition of the extraction process upon the undissolved fraction, more complete dearomatization of the feedstock can be achieved.

Having thus described my invention, what I claim is:

1. A process for selectively separating aromatic hydrocarbons from a non-viscous neutral oil containing aromatic and aliphatic hydrocarbons and boiling in the gasoline boiling range, which process comprises subjecting said oil to liquid-liquid extraction simultaneously with: (1) a dialkyl sulfone containing 2 to 4 carbon atoms, inclusive, in the molecule and having a maximum alkyl chain length of 2 carbon atoms, and (2,) water, in a proportion between about 1 and about 15% by weight based on said sulfone; separating an extract phase comprising dissolved aromatic hydrocanbons.

2. The process of claim 1 wherein said sulfone is methyl ethyl sulfone.

3. The process of methyl sulfone.

4. The process of claim 1 wherein said sulfone is diethyl sulfone.

5. The process of claim 1 wherein said sulfone is used in proportions between about 0.5 and about volumes per volume of said oil and sufiicient at least to form a distinct liquid phase and said extraction is effected at a temperature between about 0 C. and about C.

claim 1 wherein said sulfone is di- References Cited in the file of this patent UNITED STATES PATENTS 2,357,028 Shiras et al. Aug. 29, 1944 2,357,344 Morris et al. Sept. 5, 1944 2,407,820 Durrum Sept. 17, 1946 2,709,641 Gerhold May 31, 1955 

1. A PROCESS FOR SELECTIVELY SEPARATING AROMATIC HYDROCARBONS FROM A NON-VISCOUS NEUTRAL OIL CONTAINING AROMATIC AND ALIPHATIC HYDROCARBONS AND BOILING IN THE GASOLINE BOILING RANGE, WHICH PROCESS COMPRISES SUBJECTING SAID OIL TO LIQUID-LIQUID EXTRACTION SIMULTANEOUSLY WITH: (1) A DIALKYL SULFONE CONTAINING 2 TO 4 CARBON ATOMS, INCLUSIVE, IN THE MOLECULE AND HAVING A MAXIMUM ALKYL CHAIN LENGTH OF 2 CARBON ATOMS, AND (2) WATER, IN A PROPORTION BETWEEN ABOUT 1 AND ABOUT 15% BY WEIGHT BASED ON SAID SULFONE, SEPARATING AN EXTRACT PHASE COMPRISING DISSOLVED AROMATIC HYDROCARBONS. 